Lisp

(Or mythically "Lots of Irritating Superfluous Parentheses").
Artificial Intelligence's mother tongue, a symbolic,
functional, recursive language based on the ideas of
lambda-calculus, variable-length lists and trees as
fundamental data types and the interpretation of code as data
and vice-versa.

Data objects in Lisp are lists and atoms. Lists may contain
lists and atoms. Atoms are either numbers or symbols.
Programs in Lisp are themselves lists of symbols which can be
treated as data. Most implementations of Lisp allow functions
with side-effects but there is a core of Lisp which is
purely functional.

All Lisp functions and programs are expressions that return
values; this, together with the high memory use of Lisp, gave
rise to Alan Perlis's famous quip (itself a take on an Oscar
Wilde quote) that "Lisp programmers know the value of
everything and the cost of nothing".

One significant application for Lisp has been as a proof by
example that most newer languages, such as COBOL and Ada,
are full of unnecessary crocks. When the Right Thing has
already been done once, there is no justification for
bogosity in newer languages.